Profile
Every per-batch profile field: the air, the camera and the shape constants.
The profile is the world the engines run in and the camera seeing them. It rides on the material as uniforms, shared by every nozzle in one batch, and it can change while it runs: calling updateProfile every frame is fine.
Pass any subset as the batch's profile. The rest come from the batch's preset, then from these defaults (default_afterburner_profile()).
| field | default | in short |
|---|---|---|
altitudeM | 0 | How high the engines are, in metres above sea level. |
temperatureOffsetK | 0 | How much warmer the day is than the standard one, in kelvin. |
airspeedMPerS | 0 | How fast the engines move through the air, in metres per second. |
exposure | 120 | How bright the plume is drawn, as a multiplier on its radiance. |
adaptation | 0.6 | How far the camera opens up for a burner dimmer than at full power, 0 to 1. |
dryGlow | 0.35 | How bright the dry engine's glow is, as it reaches the screen. |
skyLight | 0.0005 | How much sky light the particles scatter, in the same units. |
sunLight | 0 | How much direct sunlight the particles scatter, in the same units. |
sunDirection | [0.4, 0.8, 0.45] | The direction toward the sun in world space, at any length. |
visibleTemperatureK | 850 | Below this the gas no longer glows enough to see, in kelvin. |
maxLengthD | 40 | The longest any plume is drawn, in exit diameters. |
burnerThreshold | 1 | Below this throttle the engine is on dry thrust; a rocket's is zero. |
idlePressure | 0.65 | What is left of the exit pressure at zero throttle, as a share of full. |
idleTemperature | 0.4 | What is left of the dry exhaust's heat over the air at zero throttle, as a share of what it is at military power. |
coreScale | 1 | A multiplier on the potential core length Lau's correlation gives, for the jet's Mach number and density. |
spreadScale | 1 | A multiplier on how fast the mixing layer spreads. |
shockFloor | 0.1 | How strong the shock train of a perfectly expanded nozzle still is, 0 to 1. |
shockPersistence | 1 | A multiplier on how far down the plume the shock train lasts. |
shockRelaxation | 4.5 | How quickly the gas behind a shock cools as it expands again, per cell. |
activationK | 18000 | The activation temperature of the band emission, in kelvin. |
eddyStretch | 2.5 | How much longer an eddy is than it is wide, before the shutter. |
shutterS | 1 / 60 | How long the shutter is open for, in seconds. |
meanderScale | 5 | How long a meander is, in local plume widths. |
stepSafety | 0.8 | How far a sphere trace trusts its own distance estimate, 0 to 1. |
ditherScale | 37 | How finely the march's dither is decorrelated, in inverse metres. |
altitudeM
number · default 0
How high the engines are, in metres above sea level.
The air's pressure, temperature and density follow from it through the. International Standard Atmosphere, to 86 km and isothermal above. Thin air balloons a rocket's plume and dilutes it, quenches the fuel the exhaust still carries, and bends less light.
temperatureOffsetK
number · default 0
How much warmer the day is than the standard one, in kelvin.
airspeedMPerS
number · default 0
How fast the engines move through the air, in metres per second.
Air already moving with the jet shears it less, so the mixing layer grows more slowly and the core and the shock train last further. An inlet moving that fast also rams its air, raising a jet engine's exit pressure.
exposure
number · default 120
How bright the plume is drawn, as a multiplier on its radiance.
A camera's exposure, in linear units: the radiance itself is physical, a blackbody at 2000 K having a luminance of one, and a real plume runs from a thousandth of that to a thousand times it. This picks which part of it the tone curve sees.
adaptation
number · default 0.6
How far the camera opens up for a burner dimmer than at full power, 0 to 1.
A burner just lit is far dimmer than one at the stop, its gas a few hundred kelvin cooler. A camera filming meters it and opens up, so the light-off shows. Zero holds the exposure where it is, one draws every stage as bright as full power, the colour still the gas's own.
dryGlow
number · default 0.35
How bright the dry engine's glow is, as it reaches the screen.
On dry thrust the exhaust is a thousand kelvin or less, too cool to see but as a shimmer. What shows is the hardware: the last turbine stage and the jet pipe glowing a dull red, only up the nozzle from nearly astern. Brighter the harder the engine runs, gone once the burner lights. Zero leaves a dry engine dark.
skyLight
number · default 0.0005
How much sky light the particles scatter, in the same units. The reason a solid motor's smoke is white in daylight and black at night.
sunLight
number · default 0
How much direct sunlight the particles scatter, in the same units.
Unlike the sky's, the sun's light comes from one way: smoke seen against the sun glows, seen with the sun behind the camera it is dull, and the side of a thick plume away from the sun is in its own shadow. Zero leaves the plume lit by the sky alone.
sunDirection
readonly [number, number, number] · default [0.4, 0.8, 0.45]
The direction toward the sun in world space, at any length. The position of a directional light aimed at the origin will do.
visibleTemperatureK
number · default 850
Below this the gas no longer glows enough to see, in kelvin. What the plume is cut at, where nothing in it is hot or dense enough to show.
maxLengthD
number · default 40
The longest any plume is drawn, in exit diameters. A smoky plume never ends on its own, so it is faded out by here.
burnerThreshold
number · default 1
Below this throttle the engine is on dry thrust; a rocket's is zero.
The throttle runs from 0 at idle to 1 at military power, the most the dry engine makes, and on to 1.1 at full reheat. The burner lights past here, its first zone fading in over PLUME_LIGHT_OFF and the rest staging in up to the stop.
idlePressure
number · default 0.65
What is left of the exit pressure at zero throttle, as a share of full. A rocket throttled down is a lower chamber pressure, and so a more overexpanded nozzle with a shorter, tighter shock train.
idleTemperature
number · default 0.4
What is left of the dry exhaust's heat over the air at zero throttle, as a share of what it is at military power. An idling turbine is barely warm; pushed to the detent it leaves at dryTemperatureK, still too cool for the gas to show beside the turbine's glow (dryGlow)
coreScale
number · default 1
A multiplier on the potential core length Lau's correlation gives, for the jet's Mach number and density. One is the correlation as measured.
spreadScale
number · default 1
A multiplier on how fast the mixing layer spreads.
shockFloor
number · default 0.1
How strong the shock train of a perfectly expanded nozzle still is, 0 to 1. A real nozzle is never perfectly expanded everywhere across its exit.
shockPersistence
number · default 1
A multiplier on how far down the plume the shock train lasts. At one it ends where the jet's axis stops being supersonic over the air, past which no shock can stand: see sonic_distance. Above one draws the longer trains long exposures show.
shockRelaxation
number · default 4.5
How quickly the gas behind a shock cools as it expands again, per cell. High is a sharp disk with a dark gap behind; low is a smeared glow.
activationK
number · default 18000
The activation temperature of the band emission, in kelvin. Chemiluminescence climbs very steeply with temperature, which is why the. Mach disks of a hydrogen engine glow when the rest of it barely does.
eddyStretch
number · default 2.5
How much longer an eddy is than it is wide, before the shutter.
shutterS
number · default 1 / 60
How long the shutter is open for, in seconds.
This is the motion blur, and it is what lets the exhaust move at its real speed at all: at 2000 m/s the gas crosses its own eddies many times a frame, and a camera records that as streaks, not as eddies. So the noise is stretched along the flow by exactly what the gas travels while the shutter is open, and slow gas downstream resolves into eddies while fast gas at the nozzle is the smooth streaked barrel a photograph shows.
meanderScale
number · default 5
How long a meander is, in local plume widths.
stepSafety
number · default 0.8
How far a sphere trace trusts its own distance estimate, 0 to 1.
ditherScale
number · default 37
How finely the march's dither is decorrelated, in inverse metres.